Kim Kardashian has revealed her sister Kylie Jenner has wanted her pout since she was 10 or 11-years-old, and used to say to her older sibling: "Kimmy, how come my lips aren't as big as your guys?"

Kylie revealed for the first time this week that she'd had temporary lip fillers after months of speculation, and Kim has now spoken out to support her.

Opening up about Kylie's decision during her Selfish book signing on Thursday, Kim told Access Hollywood: "What you'll see on the show is, Kylie, for a really long time, she was over-lining her lips. That was the truth for a while, then she decided to plump them."

Kylie recently revealed she's had fillers (Image: E!)

She added: "She didn't lie, it took her a while to actually make that decision to do it and once she decided to plump them, she was still over-lining, then sometimes it would look too big, then she figured out to stop over-lining.

"She plumped them and she was happy with it."

Kim went on: "People think 'Oh my god she lied for so long - now she's finally come clean' but that's not really the case, it took her a while to do it."

Kylie has had different sized lips throughout her life (Image: E!)

Kim also acknowledged Kylie is young, but fully supported her in her decision.